All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
2219.
Abies cuitlahuacii sp. nov., a mummified late Quaternary fossil wood from Chalco, Mexico
Boletin de la Sociedad Geologica Mexicana,
71
(1)
193-206
2019
ISSN: 14053322
Publisher: Instituto de GeologÃa, Universidad Nacional Autónoma de México
Abstract: ▾ A fragment of mummified wood collected from a Quaternary sedimentary sequence of Lake Chalco, Central Mexico, in the depocenter of the Basin (19°15'26"N, 98°58'32"W), has anatomical characteristics of Abies. Identification is based on the presence of a warty layer in the walls of the tracheids, prismatic crystals in ray cells, taxodioid pits in the cross-fields, and lack of ray tracheids and normal intercellular canals, among other well-preserved characteristics. This specimen represents the first macrofossil evidence of the genus in this region and suggests that by the late Quaternary it was already established in the surroundings of Lake Chalco, and most probably in what is now central Mexico. Unfortunately, as with morphological and genetic characteristics, the anatomical attributes of the wood of the genus have not been useful for the delimitation of species. Most wood characteristics have been considered of little diagnostic value. However, comparison of available anatomical descriptions of fossil and living species highlight differences among them, even with Abies religiosa wood, which is the closest species to Lake Chalco. Other characteristics or plant organs are needed to assemble a whole plant that can be used to establish phylogenetic relationships and clarify the evolutionary history of the genus. Meanwhile this wood is assigned to a new fossil taxon, Abies cuitlahuacii Cevallos-Ferriz, Ríos-Santos & Lozano-García. © Boletín de la Sociedad Geológica Mexicana 2019.
2218.
AMT survey in the Outokumpu ore belt, eastern Finland
Exploration Geophysics,
50
(4)
351 – 363
2019
ISSN: 08123985
Publisher: Taylor and Francis
Keywords:▾
Finland; Outokumpu; Pohjois-Karjala; Gold compounds; Gold deposits; Infill drilling; Magnesite; Magnetotellurics; Sulfur compounds; Surveys; Zinc deposits; 2D modelling; Airborne electromagnetic; Conductivity structures; Exploration potential; Geological interpretation; Horizontal conductors; Transverse electrics; Transverse magnetic; Archean; basement rock; fault zone; geometry; gneiss; mineral exploration; mining industry; ore body; serpentinite; Mineral exploration
Abstract: ▾ The Outokumpu belt in eastern Finland is known for numerous polymetallic (Cu-Co-Zn-Ni-Ag-Au) sulphide ore deposits and it is a potential area for new discoveries. Audiomagnetotelluric (AMT) data have recently been collected to image the subsurface conductivity structure of the belt. The data were acquired along five profiles aiming to explore deep conductors, study their geometry and investigate the deep conductivity structure of the belt.The acquired AMT data were mostly adequate for 2D inversion, as the survey area is characterised by thin, laterally extensive conductors indicated by airborne electromagnetic data, deep drillings and regional strike analysis of the impedance tensor data. 2D smooth inversion was carried out jointly for transverse electric and transverse magnetic data. The results show southeast-dipping and sub-horizontal continuous conductors southeast of the Outokumpu old mine, suggesting the presence of prospective Outokumpu assemblage rocks. One ∼ 1 km deep sub-horizontal conductor is verified by a deep drill-hole located ∼ 8 km southeast of the mine. The results demonstrate a similar southeast-dipping structure in the Vuonos mine area, which is located ∼ 7 km northeast of the Outokumpu old mine. An eastwards-dipping conductor detected in the Miihkali serpentinite area indicates deep exploration potential in this area. Besides the smooth 2D inversion, a sharp-boundary 2D inversion was performed and the resulting model was assessed with the existing geological interpretation of the Miihkali area. In the area of the Sotkuma gneiss inlier, conductors are absent from the uppermost ∼ 6 km. This feature may represent an uplifted fault block rather than a thin thrust sheet of Archaean basement rocks. © 2019 Australian Society of Exploration Geophysics.
2217.
An Analysis of Thermal Conductivity in Songliao Basin Based on Logging Parameters; [利用测井资料获取松辽盆地深部热物性参数]
Acta Geoscientica Sinica,
40
(2)
350 – 360
2019
ISSN: 10063021
Publisher: Science Press
Abstract: ▾ Thermal conductivity is an important parameter to study the deep thermal structure of the sedimentary basin. The traditional way to obtain the thermal conductivity by measurement of deep core test is limited by funding, sampling conditions and some other factors. Meanwhile, due to the reason that geothermal wells are affected by temperature and pressure conditions, indoor test results cannot represent the in-situ thermal conductivity of the rocks. In this study, the measured thermal conductivity and logging parameters of cores from 3 289 to 4 536 meters in the third spudding of well Songke 2 are obtained, and the relationship between thermal conductivity of sandstone, mudstone and rhyolite and logging parameters was analyzed. The results show that correlation between porosity, wave velocity and thermal conductivity of sandstone logging parameters is obvious, but the correlation for mudstone and rhyolite is not high. On such a basis, the authors analyzed the influence of temperature and pressure on the thermal conductivity of the Songliao Basin. It is concluded that the thermal conductivity of the third spudding of well Songke 2 in Songliao Basin is reduced by about 30% due to temperature effect, and the thermal conductivity is increased by about 10% due to pressure effect compared with 36the measured values in laboratory. The results of this study can provide a new idea for the acquisition of deep thermal conductivity and geothermal flow value of basins in China, especially for some abandoned wells with logging dates but can not obtain deep cores. © 2019, Science Press. All right reserved.
2216.
An Overview of the Status and Challenges of CO2 Storage in Minerals and Geological Formations
Frontiers in Climate,
1
2019
2215.
Anisotropic Kirchhoff pre-stack depth migration at the COSC-1 borehole, central Sweden
Geophysical Journal International,
219
(1)
66--79
2019
ISSN: 0956-540XAbstract: ▾ SUMMARY. A remarkably well preserved representation of a deeply eroded Palaeozoic orogen is found in the Scandinavian Caledonides, formed by the collision of t
2214.
Assessment of heterogeneities of the shallow crust from geophysical logging in the Koyna-Warna region, Deccan Volcanic Province, India
Physics of the Earth and Planetary Interiors,
296
2019
ISSN: 00319201
Publisher: Elsevier B.V.
Keywords:▾
Boreholes; Buildings; Exploratory boreholes; Fracture; Geophysics; Reservoirs (water); Structural geology, ATV images; Crustal heterogeneity; Fracture pattern; Geophysical logs; Koyna-Warna, Well logging, assessment method; borehole; fracture propagation; geophysical method; heterogeneity; permeability; tectonic setting, Deccan; India, Ambystoma tigrinum stebbensi virus
Abstract: ▾ Analysis and comparison of geophysical logs from seven exploratory boreholes of 1–1.5 km depth in the Koyna-Warna region of India illustrate variations in physical properties and structural characteristics of the basalts and underlying granite-gneiss basement in and around the seismogenic zone. In the north, south of the Koyna reservoir, densities are higher, gamma values are lower, fractures dip at high angles with low fracture permeabilities. To the south, around the Warna reservoir, densities are lower, gamma values higher, and resistivity values are low. In the southernmost borehole at Khadi, basement is highly fractured, and there are significant amounts of water outflow associated with the fracture system. The fracture density increases to the south, with fracture dips ranging from medium to low angles with permeability values two orders of magnitude higher than in the northern boreholes. These variations in physical and structural properties resulting in a highly heterogeneous crust, reflect the cumulative effect of episodes of tectonic activity over millions of years that this region has undergone. © 2019 Elsevier B.V.
2213.
Delineation of Damage Zones From 3 km Downhole Geophysical Logs in the Koyna Seismogenic Zone, Western India
Journal of Geophysical Research: Solid Earth,
124
(6)
6101-6120
2019
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
acoustic logging; damage; fault zone; granitoid; reservoir-induced seismicity; rock property; seismic anisotropy; seismic zone; sonic boom; stress field; structural control, India; Koyna; Maharashtra
Abstract: ▾ Delineation of subsurface faults and damage zones is a major goal of scientific drilling projects in seismically active areas. Geophysical logs acquired in a 3-km deep scientific borehole KFD1 in the Koyna seismogenic zone, a site of recurrent reservoir triggered seismicity over the past 55 years, provide an unprecedented opportunity to investigate the rock properties and delineate the fault zones. KFD1 passed through 1,247-m thick Deccan traps and continued for 1,767 m into the underlying granitic basement rocks that host the seismic activity in the depth range 2–10 km. We have studied the physical properties and acoustic behavior of basement granitoids from the analysis of geophysical logs from 1,500 to 3,000 m. Salient results are as follows. (1) Seven anomalous zones are identified below 2,100-m depth based on electrical resistivity, caliper, density, neutron porosity, self-potential, and sonic data. (2) The anomalous zones are characterized by significant shear wave velocity anisotropy (up to 25%), as revealed by cross-dipole sonic data. (3) Dispersion analysis of dipole flexural modes confirms that the anisotropy is primarily stress induced; fast polarized shear wave azimuth (FSA) therefore indicates the orientation of maximum horizontal compressive stress SHmax. (4) Comparison of FSA with independent estimates of SHmax orientations obtained from drilling induced tensile fractures and strike of inclined fractures in the anisotropic zones shows that FSA is controlled mainly by the stress regime. Therefore, the stress rotations inferred from anisotropy analyses in the anomalous zones indicate their association with subsurface fault damage zones. ©2019. American Geophysical Union. All Rights Reserved.
2212.
A method of diametrical core deformation analysis and its application on stress investigation in SK2 Well; [岩芯直径变形分析法及其在松科2井深部地应力调查中的应用]
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology),
50
(12)
3106 – 3113
2019
ISSN: 16727207
Publisher: Central South University of Technology
Keywords:▾
Deformation; Igneous rocks; Indium compounds; Instrument testing; Range finders; Stress measurement; Stresses; Complex geological condition; Core diameters; Homogeneous and isotropic; Hydraulic fracturing methods; In-situ stress measurement; Insitu stress; Maximum horizontal principal stress; Temperature environments; Stress relief
Abstract: ▾ The basic principle of diametrical core deformation analysis method(DCDA) in-situ stress testing method, core diameter testing instrument and testing process based on laser rangefinder were introduced, and the method was applied on the in-situ stress measurement of igneous rock strata on the base of 6 645-6 846 m in SK2. The results show that the core diameter curves after stress relief are sinusoidal with a periodic change of π, and the long axis and the short axis of the ellipse are nearly orthogonal. The test results conform with the theory results of DCDA method and can reflect the in-situ stress information. The direction of the elliptical long axis of core section is the direction of the maximum horizontal principal stress. According to the results of core paleomagnetic orientation, the maximum horizontal principal stress direction of 6 645-6 845 m in SK2 is determined to NE72°-83°. By taking into account the core elastic modulus and Poisson's ratio, the horizontal principal stress difference of 6 645 m in SK2 is determined to be about 35 MPa, and the horizontal principal stress difference of 6 845-6 846 m is about 55 MPa, which are almost consistent with the results of ASR in situ stress measurement. The successful application of DCDA method in the field of 6 645-6 846 m in SK2 well provides a new way to obtain the information of the deep in-situ stress, especially in the complex geological conditions of ultra deep or high temperature drilling and relatively broken formation. In this case, when the stress relief method and hydraulic fracturing method are difficult to implement, while the method can still obtain more reliable in-situ stress data. At the same time, this method is not limited by the depth and temperature environment of the borehole, and only needs nearly homogeneous and isotropic cylindrical core, and does not involve cutting and grinding the core, which is conducive to the reuse of the deep precious core. © 2019, Central South University Press. All right reserved.
2211.
Discovery of Triassic volcanic-sedimentary strata in the basement of Songliao Basin
Science Bulletin,
64
(10)
644-646
2019
ISSN: 20959273
Publisher: Elsevier B.V.
2210.
Long-term monitoring with fiber optics distributed temperature sensing at campi flegrei: The campi flegrei deep drilling project
Sensors (Switzerland),
19
(5)
2019
ISSN: 14248220
Publisher: MDPI AG
Keywords:▾
Boreholes; Boring; Environmental technology; Fiber optics; Fibers; Infill drilling; Temperature sensors; Volcanoes; Well drilling; Campi Flegrei; Continuous monitoring; Distributed temperature sensing; Environmental conditions; Hydrothermal system; Long term monitoring; Temperature calibration; Volcanic monitoring; Monitoring
Abstract: ▾ Monitoring volcanic phenomena is a key question, for both volcanological research and for civil protection purposes. This is particularly true in densely populated volcanic areas, like the Campi Flegrei caldera, which includes part of the large city of Naples (Italy). Borehole monitoring of volcanoes is the most promising way to improve classical methods of surface monitoring, although not commonly applied yet. Fiber optics technology is the most practical and suitable way to operate in such high temperature and aggressive environmental conditions. In this paper, we describe a fiber optics Distributed Temperature Sensing (DTS) sensor, which has been designed to continuously measure temperature all along a 500 m. deep well drilled in the west side of Naples (Bagnoli area), lying in the Campi Flegrei volcanic area. It has then been installed as part of the international ‘Campi Flegrei Deep Drilling Project’, and is continuously operating, giving insight on the time variation of temperature along the whole borehole depth. Such continuous monitoring of temperature can in turn indicate volcanic processes linked to magma dynamics and/or to changes in the hydrothermal system. The developed monitoring system, working at bottom temperatures higher than 100 ◦ C, demonstrates the feasibility and effectiveness of using DTS for borehole volcanic monitoring. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
2209.
Integration of underground mapping, petrology, and high-resolution microseismicity analysis to characterise weak geotechnical zones in deep South African gold mines
International Journal of Rock Mechanics and Mining Sciences,
11479 – 91
2019
2208.
Koyna, India, an ideal site for near field earthquake observations
Proceedings of the Indian National Science Academy,
85
(2)
469 – 480
2019
ISSN: 00167622
Publisher: Geological Society of India
Keywords:▾
comparative study; earthquake event; earthquake trigger; reservoir; reservoir-induced seismicity; seismic discrimination; seismograph; site investigation, India; Koyna Dam; Maharashtra
Abstract: ▾ The Koyna earthquake of M 6.3 on December 10, 1967 is the largest artificial water reservoir triggered earthquake globally. It claimed ∼ 200 human lives and devastated the Koyna township. Before the impoundment of the Shivaji Sagar Lake created by the Koyna Dam, there were no earthquakes reported from the region. Initially a few stations were operated in the region by the CentralWater and Power Research Station (CWPRS). The seismic station network grew with time and currently the National Geophysical Research Institute (NGRI), Hyderabad is operating 23 broadband seismographs and 6 bore hole seismic stations. Another reservoir, Warna, was created in 1985, which provided a further impetus to Reservoir Triggered Seismicity (RTS). Every year following the monsoon, water levels rise in the two reservoirs and there is an immediate increase in triggered earthquakes in the vicinity of Koyna-Warna reservoirs in the months of August–September. Peak RTS is observed in September and later during December.Another spurt in triggered earthquakes is observed during the draining of the reservoirs in the months of April- May. A comparative study of RTS earthquake sequences and the ones occurring in nearby regions made it possible to identify four common characteristics of RTS sequences that discriminate them from normal earthquake sequences. As the RTS events continue to occur at Koyna in a large number in a limited area of 20 km x 30 km, at shallow depths (mostly 2 to 9 km), the region being accessible for all possible observations and there being no other source of earthquakes within 100 km of Koyna Dam, it was suggested to be an ideal site for near field observations of earthquakes. This suggestion was discussed by the global community at an ICDP sponsored workshop held at Hyderabad and Koyna in 2011. There was an unanimous agreement about the suitability of the site for deep scientific drilling; however, a few additional observations/experiments were suggested. These were carried out in the following three years and another ICDP workshop was held in 2014, which totally supported setting up a borehole laboratory for near field investigations at Koyna. Location of a Pilot Bore-hole was decided on the basis of seismic activity and other logistics. The 3 km deep Pilot Borehole was spudded on December 20, 2016 and completed on June 11, 2017. © 2017, Geological Society of India.
2207.
Large-scale electrical resistivity tomography in the Cheb Basin (Eger Rift) at an International Continental Drilling Program (ICDP) monitoring site to image fluid-related structures
Solid Earth,
10
(6)
1951-1969
2019
ISSN: 18699510
Publisher: Copernicus GmbH
Keywords:▾
Buildings; Carbon dioxide; Degassing; Drilling fluids; Electric conductivity; Geophysics; Global positioning system; Infill drilling; Stratigraphy; Weathering, Continental scientific drillings; Earthquake activity; Electric resistivity tomography; Electrical resistivity tomography; Geophysical surveys; Resistivity modeling; Sensitive parameter; Stratigraphic records, Electric lines, carbon dioxide; degassing; earthquake swarm; electrical resistivity; fault zone; monitoring; tomography, Cheb Basin; Czech Republic; Karlovarsky
Abstract: ▾ <p>The Cheb Basin, a region of ongoing swarm earthquake activity in the western Czech Republic, is characterized by intense carbon dioxide degassing along two known fault zones - the N-S-striking Počatky-Plesná fault zone (PPZ) and the NW-SE-striking Mariánské Lázne fault zone (MLF). The fluid pathways for the ascending <span classCombining double low line"inline-formula">CO2</span> of mantle origin are one of the subjects of the International Continental Scientific Drilling Program (ICDP) project "Drilling the Eger Rift" in which several geophysical surveys are currently being carried out in this area to image the topmost hundreds of meters to assess the structural situation, as existing boreholes are not sufficiently deep to characterize it.</p> <p>As electrical resistivity is a sensitive parameter to the presence of conductive rock fractions as liquid fluids, clay minerals, and also metallic components, a large-scale dipole-dipole experiment using a special type of electric resistivity tomography (ERT) was carried out in June 2017 in order to image fluid-relevant structures. We used permanently placed data loggers for voltage measurements in conjunction with moving high-power current sources to generate sufficiently strong signals that could be detected all along the 6.5 <span classCombining double low line"inline-formula">km</span> long profile with 100 and 150 <span classCombining double low line"inline-formula">m</span> dipole spacings. After extensive processing of time series for voltage and current using a selective stacking approach, the pseudo-section is inverted, which results in a resistivity model that allows for reliable interpretations depths of up than 1000 <span classCombining double low line"inline-formula">m</span>.</p> <p>The subsurface resistivity image reveals the deposition and transition of the overlying Neogene Vildštejn and Cypris formations, but it also shows a very conductive basement of phyllites and granites that can be attributed to high salinity or rock alteration by these fluids in the tectonically stressed basement. Distinct, narrow pathways for <span classCombining double low line"inline-formula">CO2</span> ascent are not observed with this kind of setup, which hints at wide degassing structures over several kilometers within the crust instead. We also observed gravity and GPS data along this profile in order to constrain ERT results. A gravity anomaly of ca. <span classCombining double low line"inline-formula">-9</span> <span classCombining double low line"inline-formula">mGal</span> marks the deepest part of the Cheb Basin where the ERT profile indicates a large accumulation of conductive rocks, indicating a very deep weathering or alteration of the phyllitic basement due to the ascent of magmatic fluids such as <span classCombining double low line"inline-formula">CO2</span>. We propose a conceptual model in which certain lithologic layers act as caps for the ascending fluids based on stratigraphic records and our results from this experiment, providing a basis for future drillings in the area aimed at studying and monitoring fluids.</p>. © Author(s) 2019.
2206.
Late Quaternary lacustrine deposits of the Dead Sea basin: high resolution sequence stratigraphy from downhole logging data
Quaternary Science Reviews,
210175-189
2019
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Boreholes; Deposition; Lakes; Lithology; Sedimentology, Depositional sequences; High resolution sequence stratigraphy; Highstand systems tract; Late Pleistocene-Holocene; Sequence architectures; Sequence stratigraphy; Stratigraphic analysis; Transgressive systems tracts, Stratigraphy, data set; depositional environment; depositional sequence; lacustrine deposit; lake level; paleoclimate; Pleistocene-Holocene boundary; Quaternary; reconstruction; sequence stratigraphy, Dead Sea
Abstract: ▾ Sequence architecture and depositional sequences of the Quaternary lacustrine succession deposited in the northern Dead Sea sub-basin were examined using logging data collected during the 2010-2011 ICDP campaign. Methods borrowed from sequence stratigraphy techniques were used to investigate the characteristics of sediments deposited in the central part of the northern lake. High resolution wire logging data combined with a detailed lithological description of the ICDP 5017-1-A deep borehole were used to examine depositional systems and related processes controlling their formation. Analysis of sedimentary stacking patterns and stratal surfaces within the late Pleistocene-Holocene lacustrine succession revealed 10 depositional sequences. It was possible to identify key stratal boundaries and to discern between three sedimentary stacking patterns interpreted here as representing lowstand systems tracts (LST), transgressive systems tracts (TST) and highstand systems tracts (HST). Examined together, they may be interpreted in terms of relative lake level changes. On the basis of the stratigraphic analysis complemented with new age dating, this article presents a record of the sediment accumulation pattern and a relative lake level curve reconstructed for the last ca 225 ka. Results show that stratigraphic units and depositional and erosional surfaces examined in the deep 5017-1-A borehole can be correlated to the proximal area of the basin. This means that changes in relative lake levels were generally synchronous and uniform across the Dead Sea basin. The creation of accommodation space in the northern Dead Sea was found to generally be in phase with paleoclimatic modulating lake levels, and not due to tectonics. © 2019 Elsevier Ltd
2205.
Late-Holocene sedimentation and sodium carbonate deposition in hypersaline, alkaline Nasikie Engida, southern Kenya Rift Valley
Journal of Paleolimnology,
62
(3)
279 – 300
2019
2204.
Log response characteristics and lithological evaluation of volcanic rocks in Yingcheng Formation from the second scientific drilling borehole (SK-2 east borehole) in Songliao basin of Northeast China
Geology in China,
46
(5)
1174-1183
2019
ISSN: 1000-3657Keywords:▾
deep exploration engineering, SK-2 east borehole, volcanic rocks, log response characteristics, lithological evaluation
Abstract: ▾ <p>In order to conduct long-term deep observation, fluid experiments and investigate volcanic events in Songliao basin, the authors carried out lithological evaluation of volcanic rocks in Yingcheng Formation by using abundant and complete geophysical logs from SK-2 east borehole. The log response analysis of volcanic rocks shows that the radioactivity and electric conductivity of tuffs are the strongest. Agglomeratic lavas have low density because of high porosity. The density of rhyolites is the highest and the electric conductivity is the weakest. Volcanic rocks of Yingcheng Formation along SK-2 east borehole consist of rhyolites, transitional tuffl lavas, agglomeratic lavas and a little tuffs by using cross plots and imaging models. A volcanic eruptive gap may exist, as evidenced by tuff with high GR, low RD and low DEN. Rhyolites are characterized by high alkali, high Si, low Fe and low clay mineral. T<sub>2</sub> analysis suggests that the rhyolites are favorable for carrying out long-term observations and fluid experiments. The results provide a reference of interpretation for subsequent volcanic rock in Huoshilin Formation and research of volcanic rocks in the whole basin.</p>
2203.
Magnetic fabric development in the Lower Seve thrust from the COSC-1 drilling, Swedish Caledonides
Tectonophysics,
751212--228
2019
ISSN: 0040-1951Keywords:▾
Anisotropy of magnetic susceptibility (AMS), Crustal shear zone, Magnetic fabric, Seve nappe complex
Abstract: ▾ The COSC-1 project drilled the several hundred meters thick basal shear zone of the Lower Seve nappe with mylonites in mica schists, amphibole schists and gneisses. In zones of high magnetic susceptibility from 1910 to 2450 m we studied magnetic and petrographic fabrics, and magnetic mineralogy. Borehole imaging allowed for geographic reorientation of the samples and offered the opportunity to study anisotropy of magnetic susceptibility (AMS) in relation to tectonic evolution of the Seve thrust. We measured AMS at room temperature, added low-temperature and field-dependent AMS for a subset of samples, and compared magnetic with petrographic fabrics. Triaxial and prolate magnetic fabrics with degree of anisotropy (P′) up to 3.2 together with abundant S-C fabrics and strain partitioning around porphyroclasts indicate dominant simple shear until 2300 m. Magnetite and ilmenohematite mimic the rock fabric due to fabric parallel alignment and/or magnetic interaction and either contribute to increase or decrease of P′, depending on the dominating rock fabric elements. Field-dependency of pyrrhotite and magnetite in kmax-direction further increases P′. Homogeneous and oblate petrographic and magnetic fabrics in the greenschist-grade overprinted rocks below 2300 m with subhorizontal kmax-kint-girdle distributions indicate dominant flattening. AMS depicts shear fabrics including magnetite and ilmenohematite, and is additionally increased by retrograde magnetite-rutile intergrowth in ilmenohematites. We interpret that shape and degree of AMS are controlled by (a) tectonic deformation and strain, (b) alteration and magnetic grain interaction, and (c) field-dependency of deformed pyrrhotite and/or magnetite. We observed that all petrographic and magnetic subfabrics are coaxial, and lineations are mainly E-W to SE-NW directed confirming the transport direction of the Caledonian allochthonous. From our microstructural and AMS results we suggest that thrusting of the Lower Seve unit commenced under simple shear conditions at higher metamorphic grades and subsequently switched to more pure shear under greenschist-grade conditions.
2202.
ICDP workshop on scientific drilling of Nam Co on the Tibetan Plateau:
1~million years of paleoenvironmental history, geomicrobiology, tectonics
and paleomagnetism derived from sediments of a high-altitude lake
Scientific Drilling,
2563--70
2019
2201.
Magnetochronology of the Entire Chinle Formation (Norian Age) in a Scientific Drill Core From Petrified Forest National Park (Arizona, USA) and Implications for Regional and Global Correlations in the Late Triassic
Geochemistry, Geophysics, Geosystems,
20
(11)
4654 – 4664
2019
2200.
Medieval climate in the Eastern Mediterranean: Instability and evidence of solar forcing
Atmosphere,
10
(1)
2019
ISSN: 20734433
Publisher: MDPI AG
Keywords:▾
Chloride minerals; Drought; Floods; Food supply; Lakes; Rain; Solar radiation; Submarine geology, Climate variability; Eastern Mediterranean; Extreme events; Lake-sediment records; Medieval Climate Anomaly (MCA); Mediterranean; Northern Hemispheres; Paleoclimatic record, Climate change, aridity; climate change; climate variation; extreme event; lacustrine deposit; marine sediment; monsoon; paleoclimate; speleothem, Dead Sea; Ethiopia; Mediterranean Region
Abstract: ▾ This paper examines the hydroclimate history of the Eastern Mediterranean (EM) region during the 10th to 14th centuries C.E., a period known as the Medieval Climate Anomaly (MCA), a time of significant historical turmoil and change in the region. The study assembles several regional hydroclimatic archives, primarily the Dead Sea reconstructed lake level curve together with the recently extracted deep-lake sediment record, the Soreq Cave speleothem record and its counterpart, the EM marine sediment record and the Cairo Nilometer record of annual maximum summer flood levels in lower Egypt. The Dead Sea record is a primary indicator of the intensity of the EM cold-season storm activity while the Nilometer reflects the intensity of the late summer monsoon rains over Ethiopia. These two climate systems control the annual rainfall amounts and water availability in the two regional breadbaskets of old, in Mesopotamia and Egypt. The paleoclimate archives portray a variable MCA in both the Levant and the Ethiopian Highlands with an overall dry, early-medieval climate that turned wetter in the 12th century C.E. However, the paleoclimatic records are markedly punctuated by episodes of extreme aridity. In particular, the Dead Sea displays extreme low lake levels and significant salt deposits starting as early as the 9th century C.E. and ending in the late 11th century. The Nile summer flood levels were particularly low during the 10th and 11th centuries, as is also recorded in a large number of historical chronicles that described a large cluster of droughts that led to dire human strife associated with famine, pestilence and conflict. During that time droughts and cold spells also affected the northeastern Middle East, in Persia and Mesopotamia. Seeking an explanation for the pronounced aridity and human consequences across the entire EM, we note that the 10th-11th century events coincide with the medieval Oort Grand Solar Minimum, which came at the height of an interval of relatively high solar irradiance. Bringing together other tropical and Northern Hemisphere paleoclimatic evidence, we argue for the role of long-term variations in solar irradiance in shaping the early MCA in the EM and highlight their relevance to the present and near-term future. © 2019 by the authors.
2199.
Mediterranean winter rainfall in phase with African monsoons during the past 1.36 million years
Nature,
573
(7773)
256 – 260
2019
2198.
Mobilization of fine detritus to the Dead Sea Basin during the late glacial and early Holocene
Quaternary Science Reviews,
218395-405
2019
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Basalt; Glacial geology; Lakes; Seawater; Soils; Watersheds, Basaltic soils; Dead sea basins; Derived materials; Early Holocene; Eastern regions; Geochemical properties; Jordan valley; Last interglacial, Landforms, basalt; detritus; fine grained sediment; grain size; Holocene; late glacial; mobilization; sapropel; seafloor; submarine terrace, Dead Sea; Israel; Jordan Valley; Negev; Sahara; Southern District
Abstract: ▾ The mineralogical, grain size and geochemical properties (e.g., Nd and Sr isotopes, Mg/Al ratios) of fine detritus that accumulated in the Dead Sea during the late Glacial to early Holocene time (∼22–7 ka) are used to identify its sources and modes of transport and to reconstruct the hydroclimate conditions in the Dead Sea watershed. Samples were retrieved from the DSDDP -5017-1A core that was drilled in the deep floor of the lake, and from various exposures of surface cover in the lake's watershed. The data show that during most of the late glacial, detrital particles were either directly blown mostly from the north Sahara Desert or were washed from the surface cover (loessial soils) of the north Negev Desert and Judea Desert. This picture changed during the end of the last glacial to the early Holocene (∼14 - 7 ka) when the fine detritus showed evidence for contribution from surface cover that contained basaltic soils. The contribution of basaltic soils to the fine detritus inventory of the Dead Sea and to terraces in the Jordan Valley, indicates a period of intense erosion in the northern highlands of the Dead Sea watershed, at an interval that partly coincides with Sapropel S1. In contrast, during the last interglacial Sapropel S5, fine detritus was mostly mobilized to the lake from southern and eastern region of the watershed. The formation and accumulation of terraces from this basaltic-derived material could be an important factor in the establishment of early agriculture settlements in the Jordan Valley. © 2019 Elsevier Ltd
2197.
Modern sedimentation processes in Lake Towuti, Indonesia, revealed by the composition of surface sediments
Sedimentology,
66
(2)
675 – 698
2019
ISSN: 00370746
Publisher: Blackwell Publishing Ltd
Keywords:▾
Greater Sunda Islands; Lake Towuti; Malili Lakes; South Sulawesi; Sulawesi; Sunda Isles; Bacillariophyta; Biogeochemistry; Biological materials; Chemical analysis; Gravitation; Ocean currents; Organic compounds; Sediment transport; Sedimentation; Serpentine; Silica; Silicate minerals; Surficial sediments; Suspensions (fluids); Depositional process; Environmental conditions; Pacific warm pool; Provenance analysis; Redox condition; Sediment composition; Sedimentation process; Tropical lakes; depositional environment; lacustrine deposit; provenance; redox conditions; sediment transport; sedimentation; shallow water; Lakes
Abstract: ▾ Lake Towuti on Sulawesi Island, Indonesia, is located within the heart of the Indo-Pacific Warm Pool. This tropical lake is surrounded by ultramafic (ophiolitic) rocks and lateritic soils that create a unique ferruginous depositional setting. In order to understand modern sediment deposition in Lake Towuti, a set of 84 lake surface sediment samples was collected from across the entirety of the lake and samples were analyzed for their physical, chemical, mineralogical and biological constituents. End-member analyses were carried out to elucidate modern sediment origin, transport and depositional processes. This study found that allochthonous sediment, characterized by the concentrations of the elements Mg, Fe, Si and Al, as well as the clay and serpentine minerals, is dominated by fluvial supply from five distinct source areas. Granulometric data and the occurrence of organic matter of a terrestrial origin suggest that, in the southern and north-eastern parts of the lake the near-shore sediments may additionally be influenced by mass wasting. This is due at least partly to the particularly steep slopes in these areas. Furthermore, sediment composition suggests that sediment transport into deeper parts of the lake, particularly in the northern basin, is partly controlled by gravitational and density-driven processes such as turbidity currents. Directional sediment transport by persistent lake currents, in contrast, appears to be less important. Organic matter deposition in the ultra-oligotrophic lake, albeit limited, is dominated by autochthonous production, but with some contribution of fluvial and gravitational supply. Biogenic silica deposition, primarily from diatom frustules and sponge spicules, is very limited and is concentrated in only a few areas close to the shoreline that are characterized by shallow waters, but away from the areas of high suspension loads at the mouths of the major inlets. The results of this study build upon current and published work on short piston cores from Lake Towuti. Conversely, the results will support the interpretation of the depositional history and past climatic and environmental conditions derived from the composition of much longer records, which were obtained by the Towuti Drilling Project in May 2015 and are currently under investigation. © 2018 The Authors. Sedimentology © 2018 International Association of Sedimentologists
2196.
Effects of temperature on the frictional behavior of material from the Alpine Fault Zone, New Zealand
Tectonophysics,
76217-27
2019
ISSN: 00401951
Publisher: Elsevier B.V.
Keywords:▾
Earthquakes; Friction; Infill drilling; Stiffness; Temperature, Continental scientific drillings; Effective normal stress; Effects of temperature; Frequency distributions; Friction coefficients; High temperature; Scientific drilling; Stability boundaries, Faulting, cataclasite; drilling; earthquake; fault gouge; fault zone; friction; high temperature; rheology; stiffness; temperature effect, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ Temperature is widely believed to act as a primary control on fault rheology, and therefore on the distribution of seismicity along plate boundary faults. However, there are few detailed measurements of the frictional strength and stability of natural fault gouges at elevated temperatures. Here, we report on a suite of shearing experiments designed to investigate the frictional behavior of fault rocks sampled from depths of 111.5–142.9 m along the Alpine Fault in New Zealand obtained by the International Continental Scientific Drilling Program (ICDP) Deep Fault Drilling Project (DFDP). We tested five samples from the DFDP-1B pilot hole: two hanging wall chloritic cataclasites, two footwall granitic cataclasites, and a fault gouge from the principal slip zone (PSZ-1). Each sample was sheared at a range of temperatures from 23 to 500 °C and at an effective normal stress of 80 MPa. The wall rock cataclasites exhibit an increase in the friction coefficient (μ) with temperature, from μ = 0.45–0.64 at 23 °C to μ = 0.87 at 500 °C. The PSZ-1 gouge exhibits lower friction coefficient values than the wall rock at temperatures ≤180 °C (μ = 0.35–0.46 vs 0.45–0.65), but comparable values (μ = 0.87–0.90) at 500 °C. The variation in frictional strength is accompanied by a transition from velocity-strengthening to velocity-weakening behavior at temperatures ≥180 °C for all materials. Extrapolation of the experimentally defined rheological critical stiffness of the fault material and the estimated in situ stiffness of the surrounding crust suggests upper and lower stability boundaries at ~1.8–2.5 km and ~8.5–8.8 km depth, respectively. The upper stability boundary is also consistent with the observed depth-frequency distribution of earthquakes. © 2019
2195.
Impact-Induced Porosity and Microfracturing at the Chicxulub Impact Structure
Journal of Geophysical Research: Planets,
124
(7)
1960-1978
2019
Abstract: ▾ Porosity and its distribution in impact craters has an important effect on the petrophysical properties of impactites: seismic wave speeds and reflectivity, rock permeability, strength, and density. These properties are important for the identification of potential craters and the understanding of the process and consequences of cratering. The Chicxulub impact structure, recently drilled by the joint International Ocean Discovery Program and International Continental scientific Drilling Program Expedition 364, provides a unique opportunity to compare direct observations of impactites with geophysical observations and models. Here, we combine small-scale petrographic and petrophysical measurements with larger-scale geophysical measurements and numerical simulations of the Chicxulub impact structure. Our aim is to assess the cause of unusually high porosities within the Chicxulub peak ring and the capability of numerical impact simulations to predict the gravity signature and the distribution and texture of porosity within craters. We show that high porosities within the Chicxulub peak ring are primarily caused by shock-induced microfracturing. These fractures have preferred orientations, which can be predicted by considering the orientations of principal stresses during shock, and subsequent deformation during peak ring formation. Our results demonstrate that numerical impact simulations, implementing the Dynamic Collapse Model of peak ring formation, can accurately predict the distribution and orientation of impact-induced microfractures in large craters, which plays an important role in the geophysical signature of impact structures. ©2019. American Geophysical Union. All Rights Reserved.